The louvres are usually arranged horizontally between two vertical side members or side frames. Usually the louvres can be adjusted opened or closed by means of a pull rod. The pull rod, in the past, has been located centrally of the louvres in most cases, although in some cases there have been instances where louvre pull rods have been located at one end or the other of the louvres, alongside one or other of the side frames.
Other forms of control for the shutter louvres have been used in the past such as ladder cords, similar to the Venetian blinds, and rack and pinion systems have also been used for connecting and controlling the louvres.
Present advances in construction involve the use of extruded plastic material for the manufacture of the side frames and top and bottom frames. Also, the louvres themselves are extruded. For this purpose they are formed of hollow construction, having a generally aerofoil shape. The interior is hollow, and is formed with a variety of different interior formations, so as to maintain the aerofoil shape of the extruded louvre along its length.
Manufacturing practice with this type of construction involves cutting the louvres to length, and then fitting end closures in either end of the louvre. The end closures are usually injection moulded plastic items, and they incorporate integral fingers fitting within the louvre blade, usually enabling the end fixture to be glued in place, and they also incorporate outwardly extending axles or pivots on which the louvre blades can then be pivotally mounted between the two side members of the frame.
However, experience has shown that the use of adhesives is a time consuming messy operation, and that the need to employ special high-tech adhesives involves a very considerable cost in the manufacturing of the louvres. This is particularly true when it is considered that there may be eight or ten louvre blades, each having end fixtures at each end, meaning that up to twenty end fixtures have to be manually glued into position to make one louvre shutter. Also some end closures have tended to distort the profile of the louvre, and impair the appearance.
Accordingly, it is clearly desirable if it can be achieved, to avoid the use of adhesives, so as to both speed up production and also reduce manufacturing costs.
Another problem in the design of such shutters in the past, has been that the shutter blades were relatively heavy. Consequently, even though the individual house owner might want to have the slats open, due to the weight of the pull rod, they would gradually tend to swing closed. Another problem was that it is desirable for the sake of appearance that all of the slats shall be tilted at the same angle. Again, in the past, this was not always possible and there was a tendency for some slats to be looser and some tighter, and the looser slats might twist out of position due to air movement and the light.